Many surgical procedures require securing an implant to bone, for example, to vertebrae along the spine. Orthopedic fixation devices are frequently coupled to bone by the use of fasteners such as screws, threaded bolts, or pins. For example, bone plates can be secured to bone with bone screws, inserted through plate holes.
Securing the screws to the plate provides a fixed angle relationship between the plate and screw and reduces the incidence of loosening. Current techniques involve a locking screw that has threading on an outer surface of its head that matches with corresponding threading on the surface of a plate hole to lock the screw to the plate. Bone plates having threaded holes for accommodating locking screws are used with such screws.
For example, as a screw is being inserted into bone through the bushing and plate hole, a threaded tapered head of the screw engages a threaded internal surface of the bushing to expand the bushing against the wall of the plate hole, thereby friction locking the screw at the desired angular orientation with respect to the plate.
These multi-component traditional plate assemblies can be cumbersome and tedious to manipulate during surgery to achieve the most desirable angle for directing the bone screw into the patient.
The inventors have developed bone screws with locking mechanisms to provide retention of the screws with a bone plate and/or with the bone to prevent movement or unintended removal of the screw from the plate.